Comparative reductive desymmetrization of 2,2-disubstituted-cycloalkane-1,3-diones
摘要:
Reductive desymmetrization of 2-methyl-2-substituted-cycloalkane-1,3-diones can be effected using either NaBH(4) in DME or lithium tri-tert-butoxyaluminum hydride (LTBA) in THF at -60 degrees C. The former is a new approach that offers slightly greater diastereoselectivity in the reduction of 2,2-disubstituted-cyclopentane- 1,3-diones while LTBA is superior with 2,2-disubstituted-cyclohexane- 1,3-diones. Both conditions minimize subsequent reduction to diols thereby furnishing high yields of 1,3-ketols. Particularly rapid monoreductions are observed with 2-methyl-2-nitroethylcyclopentane-1,3-dione and 2-cyanoethyl-2-methylcyclopentane-1,3-dione when treated with NaBH(4) in DME at -60 degrees C. As expected, diastereoselectivity varies considerably with the substitution at C-2. (C) 2008 Elsevier Ltd. All rights reserved.
Pot luck: Estradiol methyl ether was synthesized using only five reaction vessels and four purification steps. The key step involved a diphenylprolinol silyl ether mediated Michael reaction. The last one-pot sequence of the reaction involves six reactions, and highlights the pot-economical aspect of the synthesis. TMS=trimethylsilyl.
Enantioselective Synthesis of Tricyclic β-Lactones by NHC-Catalyzed Desymmetrization of Cyclic 1,3-Diketones
作者:Sayan Shee、Subrata Mukherjee、Rajesh G. Gonnade、Akkattu T. Biju
DOI:10.1021/acs.orglett.0c01756
日期:2020.7.17
The NHC-catalyzed desymmetrization of cyclic-1,3-diketones allowing the enantioselective construction of tricyclic β-lactones with five contiguous stereocenters, including two quaternary stereocenters, has been developed. The mild and operationally simple addition of α-bromoenals to cyclopentane-1,3-diketone derivatives proceeds via the initial formation of chiral α,β-unsaturated acylazolium intermediates
Highly Enantioselective, Organocatalytic, and Scalable Synthesis of a Rare
<i>cis,cis</i>
‐Tricyclic Diterpenoid
作者:Daniel Townsend、Kenneth Shankland、Alex Weymouth‐Wilson、Zofia Komsta、Tim Evans、Alexander J. A. Cobb
DOI:10.1002/chem.202000164
日期:2020.3.18
A highly enantioselective, organocatalytic, and scalable synthesis of a very unusual cis-decalin-cis-hydrindane tricyclic diterpenoid system has been achieved. Despite the prevalent pharmacological space that the related trans,trans and trans,cis-systems occupy, there have been no reports of an asymmetric synthesis of the cis,cis systems in the literature until now. We demonstrate the flexibility of
Triethylamine-Promoted Henry Reaction/Elimination of HNO<sub>2</sub>/Cyclization Sequence of Functionalized Nitroalkanes and 2-Oxoaldehydes: Diversity-Oriented Synthesis of Oxacycles
作者:Yu-Xia Lu、Xue-Jiao Lv、Chang Liu、Yan-Kai Liu
DOI:10.1021/acs.orglett.3c01158
日期:2023.6.9
The triethylamine-promoted cascade Henry reaction/elimination of HNO2/cyclization reaction of 2-oxoaldehydes with nitroalkanes bearing various remote functionalities is described. Both chiral and achiral nitroalkanes were applicable to this protocol, leading to a variety of oxacycles, such as chromenes, chromanes, cyclic hemiacetals, and polycyclic acetals. An unexpected regioselective photooxygenation
Asymmetric Flow Reactions Catalyzed by Immobilized Diphenylprolinol Alkyl Ether: Michael Reaction and Domino Reactions
作者:Yujiro Hayashi、Shusuke Hattori、Seitaro Koshino
DOI:10.1002/asia.202200314
日期:2022.7.15
Immobilized diphenylprolinol alkyl ether catalyst was found to be effective for the flow reactions. Three flow reactions were examined. Good overall yield (72%), excellent enantioselectivity (93% ee), and good turnover number (TON, 495) were obtained for a 61 h flow Michaelreaction of nitromethane and cinnamaldehyde.
发现固定的二苯基脯氨醇烷基醚催化剂对流动反应是有效的。检查了三个流动反应。对于硝基甲烷和肉桂醛的 61 小时流动迈克尔反应,获得了良好的总产率 (72%)、出色的对映选择性 (93% ee ) 和良好的周转数 (TON, 495)。